Beware of Raw Cookie Dough

By ANAHAD O'CONNOR

December 12, 2011

Turns out mom was right: Keep your hands off the raw cookie dough.

A new study that investigated the cause of a large outbreak of E. coli in 2009 pointed the blame at raw chocolate chip cookie dough. The researchers say it is the first time an outbreak of food poisoning caused by the dangerous Shiga toxin-producing E. coli has been traced to store-bought, ready-to-bake cookie dough or a similar product. The outbreak, between March and July 2009, sickened at least 80 people across 30 states, 35 of whom had to be hospitalized.

Anyone who has ever baked homemade cookies knows how tempting the batter can be. And although most people are aware that sneaking a bite carries a risk, that knowledge apparently is not much of a deterrent. A 2008 study of risky eating behaviors among college students found that 53 percent admitted to eating unbaked homemade cookie dough.

Prudent chefs and parents everywhere usually cite a single cookie dough ingredient – raw eggs, which can carry Salmonella – as the reason to bake before eating. But the study, led by Dr. Karen Neil, a medical epidemiologist with the Centers for Disease Control and Prevention, found that the culprit in this case was likely not eggs, but flour.

“Out of all the ingredients, raw flour is the only raw agricultural product that was in the cookie dough,” Dr. Neil said. “It didn’t undergo any specific processing to kill pathogens, so we feel that’s the most likely suspect for what may have introduced contamination into the cookie dough. We couldn’t prove it conclusively, but that’s what we suspect.”

As with many commercial food products, the eggs used in the contaminated cookie dough were pasteurized, a process that kills pathogens. The molasses, sugar, baking soda and margarine used in the dough also underwent “pathogen kill steps” during processing that made them unlikely to be sources of the contamination, and the chocolate chips used in the dough revealed no evidence of E. coli, the researchers found.

One study that looked at commercial wheat flour samples found almost 13 percent contaminated with E. coli. The investigators also pointed out that wheat flour can also be contaminated with Salmonella, and that flour-based mixes have previously been implicated in outbreaks of food-borne illness.

Home cooks who prefer making their own batter should still be just as wary of consuming unbaked cookie dough, especially because of the Salmonella risk from raw eggs, Dr. Neil added.

“It’s difficult to do a direct comparison of the risks,” she said, “but the bottom line is consumers should not eat raw cookie dough, or really any other raw product that’s intended to be baked or cooked before consumption.”

“I think the safest thing people can do is just practice good safety measures in general,” she said. “The four basic messages we use are clean, separate, cook and chill.” For more information, visit the government Web site foodsafety.gov.